Theoretical and mathematical physics students – postgradual studies

Cílem práce je studium kvasarového mikročočkování, konkrétně přechodu akrečního disku kvasaru přes kaustiky vytvářené gravitačním polem hvězd čočkující galaxie. Na základě simulací bude student analyzovat souvislost fotometrických a spektroskopických pozorování přechodu s prostorově rozlišenou strukturou emise disku.

Student by se měl seznámit s teorií rozptylu v nerelativistické kvantové mechanice a jejími aplikacemi na srážky elektronů s molekulami a záporných iontů s atomy. Cílem práce je podrobné studium konkrétních systémů, při nichž hraje důležitou roli tvorba záporných molekulových iontů. Úplný kvantový popis dynamiky těchto iontů vede na výpočty v rámci tzv. nelokálního rezonančního modelu a je zásadní pro výpočty účinných průřezů rezonančních procesů, jako jsou vibrační excitace molekul při srážkách...

Náplní doktorské práce bude podrobné studium klasických a kvantových jevů v obecné relativitě. Student se detailně seznámí s existující literaturou na téma izolovaných horizontů, což je koncept černých děr v rovnováze s okolím, který zobecňuje klasická řešení jako je Schwarzschildovo nebo Kerrovo řešení. Na klasické úrovni, se bude jednat zejména o studium trojrozměrné geometrie těchto horizontů, výpočet kvazi-lokálních multipólových momentů izolovaných horizontů a jejich vztah k standardním Ger...

Theoretical description of electron-molecule collisions still represents a great challenge. This problem is closely related to the theory of reactive collisions of negative ions. In addition to involving many particles, this theory is complicated by the contribution of electron continuum and breakage of the Born-Oppenheimer approximation. All these problems are properly solved in the nonlocal resonance model theory. This theory is used only for diatomic molecules. For triatomic molecules the theory has been used only in the local complex potential approximation [5]. Goal of this work is to contribute to the solution of triatomic collisions beyond the Born-Oppenheimer approximation.

Student se seznámí s několika přístupy ke kanonickému kvantování prostoročasů. Jednat se bude zejména o metodu založenou na Wheelerově-deWittově rovnici, dále o její modifikaci vycházející z použití symetrií superprostoru na kvantové úrovni a následně o smyčkové metody kvantování v rámci sférické symetrie. Rozšíření za rámec sférické symetrie může být provedeno hybridním kvantováním, kdy se stupně volnosti popisující odchylku od symetrické situace řeší pomocí Fockova kvantování.

Cílem této práce je rozvíjet metody pro numerické řešení rovnic popisujících kvantovou reakční dynamiku rozptylu elektronů, atomů, molekul a iontů. Řešitel prostuduje metody používané pro řešení této dynamiky vycházející budˇ z řešení Schrodingerovy rovnice se správnou okrajovou podmínkou, nebo z integrálních rovnic teorie rozptylu (Lippmann-Schwingerova rovnice, Faddeevovy rovnice) a napíše vlastní numerický program, který otestuje nejdříve na problémech s nižší dimenzionalitou. Hotovou metodu použije pro výpočet účinných průřezů a rekčních rychlostí pro vhodný systém aplikovatelný v problémech fyziky plazmatu, radiačního poškození biomolekul nebo astrofyziky.

Nedávno zveřejněný "snímek" černé díry v jádře galaxie M87 potvrdil, že možnosti detektorů se rozšířily na samotné hranice (horizonty) těchto extrémních objektů. Díky robustnosti obecně relativistické předpovědi nebylo překvapením, že jí publikovaný obrázek velmi dobře odpovídá, nicméně snaha o zpřesnění observačních dat bude dále pokračovat, aby bylo možno kvantifikovat, do jaké míry odpovídají podobné objekty černým dírám popsaným Kerrovým řešením, a určit jejich parametry. Reálné černé díry r...

Cílem práce je studium souvislosti entangement entropie s velikostí extremální nadplochy v rámci AdS/CFT korespondence ve zjednodušeném 2+1 dimenzionálním modelu.

With the discovery of gravitational waves from merging compact object binaries and the associated electromagnetic signatures there has been renewed interest in properly understanding and characterizing binary star evolution and especially its violent phases such as common envelope evolution. At the same time, astronomy has witnessed a tremendous growth of available data thanks to dedicated time-domain surveys. The goal of this project is to provide novel constraints on the critical binary star evolutionary phases on the interface of complex data modeling and theoretical inquiry.

Od začátku práce na disertaci studovat níže doporučenou a sledovat nově se objevující literaturu. V původní práci se nejprve v rámci speciální teorie relativity zaměřit na "vrstevnatá" prostředí, která se pohybují s měnící se velikostí rychlosti ve stejném směru a šíření záření dopadajícího v kolmém směru na tyto vrstvy. Prostředí má jak refraktivní tak disperzivní vlastnosti. Zobecnit úlohu i na diferenciálně rotující prostředí. Vhodně vykreslit trajektorie paprsků pro různé rychlosti prostředí...

Thermodynamics of spacetime.

Geodesic motion is completely integrable in the fields of isolated stationary black holes, but it may become chaotic if there exists some additional source in the space-time. Motivated by accreting black holes in astrophysics, we have studied the geodesic dynamics in the field of a Schwarzschild black hole encircled by a thin disc or a ring (see [1] for the last paper of our series devoted to this topic). Hitherto, we restricted the problem to the static and axisymmetric case. However, accreting...

The goal of the thesis is to significantly develop understanding of the theory and observational implications of two stars undergoing strong interaction or a merger. Depending on the interests of the student, the work will focus on understanding unusual transients likely associated with binary star interactions, transients from stellar collisions, formation of dust and molecules in binary interactions, and understanding the observational implications of the theory (blue stragglers, R CrB stars, ...

In astrophysics, matter is being accelerated by various forces and mechanisms. One of the most exciting environments where the accelerating mechanisms are not yet fully understood is the accreting black hole. Besides the gravitational effect, the matter in such a system is most notably subject to magnetohydrodynamical processes (including collisions of streams, shock waves, energy release due to magnetic reconnection, etc.) and to an interaction with radiation. In many accreting systems, the int...

This thesis is focused on advancing the theory of binary star interactions. The immediate goal is to revisit the prescriptions for mass transfer in close binaries and investigate their influence on runaway phases of binary star evolution culminating in common envelope events. This evolutionary pathway is of great importance for producing many important astrophysical objects, including gravitational wave sources like binary black holes and double neutron stars. Depending on the interest of the st...

Student prozkoumá obecné vlastnosti geometrií charakterizovaných přítomností světelné geodetické kongruence s nulovým twistem. Analyzuje jejich algebraickou strukturu a chování volných testovacích částic. Dále se zaměří na studium explicitních prostoročasů této třídy v obecné relativitě a jejích zobecněních.

The origin of gravitational wave sources (binary black holes and double neutron stars on close orbits) is one of the most captivating problems of contemporary astrophysics. Perhaps the most explored evolutionary scenario involves a common envelope evolution episode in an isolated binary star. A new window into this phase has been provided by steadily growing number of luminous red novae (LRNe)/intermediate luminosity optical transients (ILOTs). The immediate goal of this thesis is to perform mul...

The aim of this work will be the study of exact spacetimes of gravity theory in three dimensions, and their comparison with analogous solutions of Einstein’s field equations in general relativity in four and higher dimensions. The main topic will be an algebraic classification, geometric analysis, and physical interpretation of the complete class of solutions which were found in our recent works, involving all such spacetimes without matter (including any value of the cosmological constant), with pure radiation (possibly with a gyratonic sources), and also electromagnetic field.

The student will: 1) Explore new venues for hidden symmetries and their applications to black hole physics and beyond, and 2) Understand black hole chemistry in the context of the AdS/CFT correspondence, and study its implications for black hole microstructure and black hole phase transitions.

The student working on this project will attack some of the following problems. 1) Understand the black hole chemistry in the context of the AdS/CFT correspondence, and its implications for black hole microstructure. 2) Explore new venues for hidden symmetries and their applications. 3) Probe modified gravity theories. 4) Study quantum information aspects of curved spacetimes.

The detection of gravitational waves (GW) has revolutionized our way of observing the Universe. Thanks to GW signals, we can now explore features of astrophysical objects which were impossible to detect only a few years ago. In particular, we can probe deeper into the structure of compact relativistic objects and their evolution. Such an advance in detection measurement requires an equal advance in theoretical tools within which such objects can be understood. This project aims to develop such ...

Student se seznámí s teoriemi rozšiřujícími Einsteinovu obecnou relativitu o korekce vyšších řádů. Bude analyzovat a zobecňovat vhodné metody řešení rovnic gravitačního pole spolu se studiem konkrétních prostoročasů a jejich fyzikálních a matematických vlastností.

The goal of the thesis is to study spacetimes containing more than one black hole. The student will explore possible static or stationary configurations of multiple black holes with diverse asymptotics and possibly immersed in various external fields. They will also attempt to extend to higher dimensions previous analyses of slow-motion perturbations of static multi black-hole spacetimes.

Terms with derivatives of higher order appear naturally in many effective descriptions of quantum gravity. They tend to resolve or mitigate issues related to ultraviolet incompleteness of general relativity such as the existence of spacetime singularities and quantum non-renormalizability. Higher-derivative theories of finite order suffer from Ostrogradsky instability, which manifests in the presence of ghost degrees of freedom at the linear level [1]. Gravitational theories can be rendered ghos...

A body of finite mass moving in an ambient space-time will never move on a geodesic of said space-time; it will perturb the space-time, and this will back-react on its motion. In many physical settings this leads to the emission of gravitational waves and a merger of the components of the system. Similarly, a charge moving in an electromagnetic field or a color-charge moving in a Yang-Mills field will never quite move as a test particle; it will also back-react on its own motion. All these effec...

Gravitational lensing serves as an invaluable tool for studying the distribution of mat- ter in the universe. This matter is predominantly dark and clumped into centrally concen- trated hierarchically structured halos of galaxies and galaxy clusters. Early comparisons suggested discrepancies between the high population of substructures predicted by cos- mological simulations and the lack of corresponding observational data. More recently, a major discrepancy in the opposite sense was reported fr...

In this thesis, we study two distinct topics both connected to stationary axially sym- metric spacetimes. The first is a study of an exact solution sourced by phantom scalar field. This solution can be derived from the well-known Curzon-Chazy metric and has several unusual features. It is a spherically symmetric wormhole which is however not symmetric with respect to its throat, it possesses a non-scalar curvature singularity and functions as a one-directional time machine. The energy content of...

In this thesis, we study exact black hole spacetimes of algebraic type D, which are a part of much wider Pleba'nski-Demia'nski class of solutions. We reformulate the well- known form of this metric and obtain new improved representation of this black hole family with simplified, explicit and (at least partially) factorized metric functions. This new form of the spacetimes allows us to gain the standard expressions for the well-known solutions such as the Kerr-Newman-NUT-(anti-)de Sitter black ho...

Future space-based gravitational-wave detectors will require highly accurate gravi- tational wave templates for detecting extreme mass ratio inspirals and estimating their parameters. These templates must include the postadiabatic effects like the spin of the secondary body. Therefore, we investigate the influence of the secondary spin on the motion around a Kerr black hole, calculate the corresponding gravitational-wave fluxes to produce flux-driven inspirals and reveal the shifts of the gravit...

In this thesis, we study a limit of the Kerr-(A)dS spacetime in a general dimen- sion where an arbitrary number of its rotational parameters is set equal. The resulting metric after the limit formally splits into two parts: the first part has the form of the Kerr-NUT-(A)dS metric analogous to the metric of the entire spacetime, but only for the directions not subjected to the limit, and the second part can be interpreted as the Kähler metrics. However, this separation is only valid for tangent s...

Choptuik's unexpected discovery, almost 30 years ago, of critical behavior in grav- itational collapse opened a whole new research area within numerical relativity. While critical collapse in spherical symmetry has been thoroughly investigated and is reasonably well understood, progress for axial symmetry has been much slower. In this thesis, we study axially symmetric gravitational collapse of gravi- tational waves using numerical simulations. We construct several very different initial data families and investigate their behavior close to the threshold of collapse. We compare them against each other and also against other published results. We use invariant quantities to look for signs of self-similarity and universality.

Collisions of low-energy electrons with molecules lead to excitation of vibrational degrees of freedom or even to bond dissociation. Such phenomena are not fully understood in the case of polyatomic targets since the theoretical treatment is complicated by the multidimensionality of the vibrational dynamics and the interaction of multiple short- lived electronic states. In this thesis, we extend the nonlocal theory of these processes by considering the vibronic coupling through the electron cont...

Motivated by our desire to find generalizations of the Bonnor-Melvin spacetime, the thesis investigates seven static, cylindrically-symmetric and electrovacuum exact solutions to the Einstein-Maxwell equations. They contain a magnetic field and six of them also include the cosmological constant. After discussing some of the methods we use during our investigation, we present the basic properties of the spacetimes, and for each of them we also study charged test particle motion and their admissible shell sources composed of particle streams. We also perform numerical computations to determine whether the equations admit more general solutions than the exact ones we derived.

The aim of this thesis is to construct exact, axially symmetric solutions of Einstein- Maxwell(-dilaton) equations, which possess a discrete translational symmetry along an axis. We present two possible approaches to their construction. The first one is to solve Einstein-Maxwell equations, the second one relies on a dimensional reduction from a higher dimension. We examine the geometry of the solutions, their horizons and singu- larities, motions of charged test particles and compare them.

In this work, we studied three selected problems in FRW spacetime. In the first part, we analysed the motion of a test particle in the homogeneous and isotropic universe. We presented a framework in which one can derive the uniformly accelerated trajectory and geodesic motion if a scale factor for a given spacetime is provided as a function of coordinate time. By applying the confomal time transformation, we were able to convert second order differential equations of motion in FRW spacetime to f...

In this work we study properties of spacetimes with a high degree of symme- try. Particularly, we focus on geometries related to higher-dimensional rotating black-hole spacetimes described by the Kerr-NUT-(A)dS metric. In the first part, we examine spacetimes admitting a separable Klein-Gordon equation. Motivated by Carter's work in four dimensions, we introduce a separable met- ric ansatz in higher dimensions. Analyzing Einstein's equations, we obtain the Kerr-NUT-(A)dS and specific Einstein-K¨...

In this work, we study geometrical and physical properties of exact spacetimes that belong to non-expanding Pleba'nski-Demia'nski class. It is a family of solutions of type D that also belong to the Kundt class, and contain seven arbitrary parameters including a cosmological constant. We present here the results of three extensive articles, each focusing on a different aspect of the problem. In the first article, we investigate the meaning of individual parame- ters in the non-expanding Pleba'ns...

Jakub Benda Astrophysically important processes in collisions of electrons with hydrogen atoms This thesis focuses on calculations of the cross sections and other scattering quantities that characterize the outcome of collisions of electrons with hydro- gen atoms. For the chosen energy range and atomic transitions the scattering process is solved within the non-relativistic quantum mechanics by discretiz- ation of the Schr¨odinger equation in the basis of B-splines, which transforms the equation...

Cílem práce je 1) podat ucelený přehled topologií kritických křivek a kaustik trojité gravitační mikročočky; 2) prozkoumat chování mapy zjasnění v blízkosti jednotlivých částí kaustiky; 3) studovat zjasnění nebodového zdroje, citlivost čočky na nebodovost a okrajové ztemnění zdroje; 4) uplatnit zjištěné výsledky na pozorovaných případech trojitých mikročoček.

Podrobně rozebrat a porovnat různé způsoby středování používané v nehomogenních kosmologických modelech a pro vysvětlení různých astrofyzikálních jevů (např. galaktických rotačních křivek). Dokončit vývoj středovacího postupu navrženého v rámci diplomové práce a aplikovat ho v zajímavých netriviálních situacích. Pokusit se použít programy pro algebraické manipulace ke zjednodušení výpočtů s Cartanovými skaláry, na kterých je vyvýjená metoda založena. Prostudovat vazbu středování nehomogenit na astrofyzikální efekty standardně vysvětlované pomocí temné hmoty a temné energie. Prozkoumat generování symetrií původně obecného nehomogenního prostoročasu při specifickém středování.